The invention relates to an internal combustion engine with at least one control element for variation of the flow cross-section of a charge exchange passage, which control element is automatically adjustable in accordance with the engine mode by means of an actuating member and a connecting element.
With the use of this control element it is possible during engine operation to vary the exhaust timing and the amount of exhaust gases discharged, for instance. In this way the torque curve may be flattened, yielding good torque values at low engine speed and improving acceleration of the engine when the control element is turned in closing direction, while the open control element ensures high power output. So far the control element has been actuated in accordance with the number of revolutions or engine speed, using a centrifugal governor device (U.S. Pat. No. 4,368,703) or an electric or hydraulic servomotor and corresponding control device (U.S. Pat. No. 4,516,540). Other attempts include actuation of the control element via a membrane, in accordance with the pressure prevailing in the exhaust system. All these variants are technically complex without permitting automatic adjustment of a mechanically actuated control element in dependence of engine speed and load. Another known design of a two-stroke engine provides that the crankside edge of the intake port be adjusted by a control body in stroke direction in order to achieve satisfactory pre-compression during start-up and in the lower speed range and prevent a return flow of air or charge mixture into the intake port (DE 36 37 883 A1), but this control element, which is provided on the intake side, once more is actuated by a servomotor.
EP 0 413 317 A1 shows an exhaust valve system for a two-stroke engine with several cylinders. Transfer and exhaust ports are staggered around the cylinder axis to permit a compact design. Each exhaust passage contains a control element for flow control, which is actuated by a servomotor.
It is the object of the present invention to eliminate this deficiency and provide an internal combustion engine of the afore-mentioned type wherein adjustment of the control element is effected by simple means in dependence of engine torque.
According to the invention this object is achieved by providing that the internal combustion engine be flexibly supported in a frame, and that the actuating member of the control element be supported via the connecting element on at least one pivot fixed in the frame, such that the control element can adjust itself with increasing torque, due to the relative movement between engine and frame resulting from the torque of the combustion engine, thereby increasing the flow cross-section of the charge exchange passage while varying the beginning of the charge changing process.
Preferably, a first control element is provided in at least one charge exchange passage configured as an exhaust passage, which control element can be actuated by supporting it on a pivot fixed inside the frame.
An engine that is flexibly supported in a frame is characterized by a certain rotatory and/or translatory degree of freedom decreasing with an increase in torque. Hence a relative movement between the engine and its frame will result, which may be utilized for actuation of the first control element varying the flow cross-section of the exhaust port. This first control element will open when the engine is operating at high load, thus uncovering a larger cross-section of the exhaust port for a prolonged period of time and resulting in higher torque values at higher engine speeds. Adjustment of the control element takes place fully automatically in dependence of engine load and speed.
Above all engines operating on the two-stroke cycle may be provided with a second control element located in the intake passage, which will also be actuated by supporting it on a pivot fixed in the frame. The second control element, which is actuated in the same manner as the first control element and is located in the intake passage controlled by the piston edge on the side of the crank, will raise the charge level when the engine speed is high and the control element in open position, and advance pre-compression and thus increase the engine torque when the speed is low and the flow cross-section of the intake port is reduced.
A particularly simple design will be obtained if the control element is configured as a flap turning about an edge or a central axis.
In a two-stroke internal combustion engine with at least one charge exchange passage configured as a transfer passage it may be provided that a third control element be positioned in the at least one charge exchange passage configured as a transfer passage, which also may be actuated by supporting it on a pivot fixed in the frame.
For an engine operating on the two-stroke cycle it will be of advantage if the control element is capable of varying the flow cross-section of the exhaust passage and/or the intake passage in the direction of the cylinder axis. In order to achieve an effective flow control of the flow through the exhaust passage, it is proposed that the first control element configured as a one-sided flap be held at the top side of the exhaust passage next to the top of the combustion chamber. It may further be provided that the second control element configured as a one-sided flap be held at the bottom side of the intake passage distant from the top of the combustion chamber. If the first and/or second control element is at least partially closed, the above measures will induce the control edge of the piston first of all to uncover the half of the exhaust port and/or intake port covered by the flap, thus preventing short-circuiting due to the partially closed cross-section.
The proposed flow control system will not be limited to two-stroke engines but will also be useful with four-stroke engines. In this case the first control element is positioned downstream of the exhaust valve, and preferably in the area of an exhaust flange.